Stefano Domenicali believes Sebastian Vettel deserved his drive-through penalty in the Italian Grand Prix and revealed that Fernando Alonso's car was damaged in the incident.

Alonso was forced on to the grass when trying to overtake Vettel through Curva Grande and had to lift to rejoin before later overtaking the Red Bull. Vettel was given a drive-through penalty for the incident and Domenicali revealed that it could have ended Alonso's race due to damage he sustained by going off track.

"When Alonso went off track as he was attacking Vettel ... that caused him some damage at the rear which unfortunately got worse with every lap, so we had to keep an eye on that," Domenicali said. "You never know how much a car can put up with so the end of the race was a real cliffhanger.

"We had a problem with the car. In fact if you see the car there is very big damage on the rear - on the left rear - and we had also a problem with something broken from the mechanical point of view. So we were trying to manage that situation, telling him at the end not to go over the kerbs because it could have made the problem bigger."

With some observers pointing to a similar incident when Vettel went on to the grass overtaking Alonso in the same corner last year, Domenicali said a recent clarification meant the two incidents were being judged differently.

"After what happened in Bahrain there was a clarification from race control that the driver in front has to leave space if there is a part of the car that's approaching that is already beside the car. So technically speaking there is nothing to say, it was exactly what is written in the regulation.

"I heard 'Why was last year not penalised?' All I can say is it's a different situation if you look in slow motion - although it's not really correct to look at these things in slow motion because they're racing at 300kph - it's totally different and this year it's a different rule."